With increasing development of science and technology, the applications of various electronic devices become more and more diversified. As known, the performance of the electronic device used by the consumer is highly dependent on whether the quality control specification in the production line of electronic device is strict or not. For example, in the production line of an image pickup device such as a web camera or a camera, the installation and setting of the lens thereof affect the image quality of the image pickup device.
FIG. 1 schematically illustrates a portion of a conventional image pickup device. As shown in FIG. 1, the image pickup device 1 comprises a lens 11 and a sensing element 12. For example, the sensing element 12 is a charge-coupled device (CCD). The image frame captured by the lens 11 can be imaged on the sensing element 12. Consequently, during the process of assembling the lens 11, the lens 11 needs to be parallel with the sensing element 12 as possible as it can. In such way, the image frame outputted from the sensing element 12 is not distorted, or the image frame is not partially shape or partially blurred.
Conventionally, in the production line of the image pickup device 1, the focus of the lens 11 is adjusted before the lens 11 is assembled. For assuring that the lens 11 of the assembled image pickup device 1 is parallel with the sensing element 12, an image pickup operation is performed to shoot an object 8, and thus an image frame 9 is obtained (see FIG. 2). The object 8 is usually a planar picture, which is placed on a jig tool (not shown) of a production line. The planar picture is adjusted to be parallel with the sensing element 12 of the image pickup device 1.
Please refer to FIG. 2, which is a schematic view illustrating an image frame captured by the conventional image pickup device. The image frame 9 captured by the image pickup device 1 will be outputted to an electronic computing device such as a computer. By an application program executed in the electronic computing device, the image frame 9 is divided into a plurality of sub-image blocks 91˜99. Moreover, by the application program, the resolution values of these sub-image blocks 91˜99 are analyzed, and each of the resolution values is compared with a preset threshold value. In a case that the resolution value of any of the sub-image blocks is lower than the preset threshold value, it means that the lens 11 of the image pickup device 1 is not parallel with the sensing element 12 and the sub-image block is blurred. Under this circumstance, it is necessary to re-install the lens 11 of the image pickup device 1 until the resolution values of these sub-image blocks 91˜99 are all higher than the preset threshold value.
Moreover, the resolution values of these sub-image blocks 91˜99 are calculated on the basis of a modulation transfer function (MTF), and the resolution values can be referred as MTF values. As the MTF value is increased, the black and white contrast is increased, and thus the image is sharper. Whereas, as the MTF value is decreased, the black and white contrast is decreased, and thus the image is more blurred. That is, if the MTF values of the sub-image blocks 91˜99 are all higher than the preset threshold value, it means that the whole image frame 9 is sharp and qualified. Under this circumstance, it is determined that the lens 11 and the sensing element 12 of the assembled image pickup device 1 are parallel with each other.
Nowadays, since the imaging technology of the image pickup device 1 is increasingly developed, the lens 11 of the commercially available image pickup device 1 has enhanced resolution. Due to the good resolution of the image pickup device 1, regardless of whether the lens 11 and the sensing element 12 of the image pickup device 1 are parallel with each other or not, the resolution values of all of the sub-image blocks 91˜99 of the image frame 9 are significantly distinguished. In other words, the accuracy of judging whether the lens 11 and the sensing element 12 of the image pickup device 1 are parallel with each other in the production line will be impaired. Therefore, there is a need of providing an improved method for judging whether the lens 11 and the sensing element 12 of the image pickup device 1 are parallel with each other.